1. Technical Field
The present disclosure relates to a display device including a touch screen, in which touch sensors are embedded in a pixel array, and a driving circuit for driving the display device.
2. Discussion of the Related Art
User interfaces (UIs) are configured to allow users to communicate with various electronic devices and to easily and comfortably control the electronic devices as they desire. Examples of UIs include a keypad, a keyboard, a mouse, an on-screen display (OSD), and a remote controller having an infrared communication function or a radio frequency (RF) communication function. User interface technology has continuously expanded to increase user's sensibility and handling convenience. UIs have been recently developed to include touch UIs, voice recognition UIs, 3D UIs, and the like.
A touch UI senses a touch input (or a user input) using a touch screen implemented on a display panel and transmits the touch input to an electronic device. The touch UI has been essentially adopted in portable information devices, such as smart phones, and use of the touch UI has been expanded to include uses in notebook computers, computer monitors, and home appliances.
A method for implementing a touch screen has been recently employed using a technology (hereinafter referred to as “in-cell touch sensor technology”) for embedding touch sensors in a pixel array of a display panel. The touch sensors may be implemented as capacitive touch sensors sensing a touch input based on changes in a capacitance before and after the touch input.
In in-cell touch sensor technology, touch sensors may be installed in a display panel without an increase in a thickness of the display panel. Electrodes of pixels of the display panel may be used as touch electrodes of the touch sensors. As shown in FIG. 1, in the in-cell touch sensor technology, a common electrode for supplying a common voltage Vcom to pixels of a liquid crystal display may be divided to form touch electrodes C1 to C4. The touch electrodes C1 to C4 are connected to sensor lines SL. Because touch sensors Cs are embedded in a pixel array of a display panel, the touch sensors Cs are coupled with pixels through parasitic capacitances. In order to reduce signal interference (e.g., cross talk) attributable to coupling between the pixels and the touch sensors Cs in the in-cell touch sensor technology, one frame period is time-divided into a display period and a touch sensing period. The in-cell touch sensor technology supplies a reference voltage (i.e., the common voltage Vcom) of the pixel to the touch electrodes C1 to C4 during the display period and drives the touch sensors Cs and senses a touch input during the touch sensing period.
A display device includes a data driver supplying a data voltage to data lines of a display panel, a gate driver (also referred to as a gate driver circuit or a scan driver) supplying a gate pulse (also referred to as a scan pulse) to gate lines of the display panel, and a touch sensing unit (also referred to as a touch sensing circuit or touch driver circuit) driving touch sensors.
The gate driver sequentially shifts the gate pulse applied to the gate lines using a shift register. The gate pulse is synchronized with the data voltage (i.e., a pixel voltage) of an input image and sequentially selects each pixel to be charged to the data voltage. The shift register includes cascade-connected stages. The stages of the shift register receive a start signal or a carry signal received from a previous stage as the start signal and generate an output when a clock is input.
A screen of the display device may be divided into two or more blocks, and a touch sensing period may be assigned between a driving time of one block and a driving time of another block. For example, during a first display period, pixels of a first block may be driven, and data of the first block may be updated to current frame data. During a touch sensing period following the first display period, a touch input may be sensed. During a second display period following the touch sensing period, pixels of a second block may be driven, and data of the second block may be updated to current frame data. However, such a method may deteriorate the output characteristic of the gate pulse supplied to the gate lines, and as a result, lead to a reduction in image quality of the display device.
In the second block driven immediately after the touch sensing period, a voltage of a Q node at a stage of a shift register outputting a first gate pulse may be discharged during the touch sensing period due to a leakage current. Because the Q node is connected to a gate of a pull-up transistor, a decrease in the voltage of the Q node may make the bootstrapping of the pull-up transistor incomplete. Hence, the gate pulse, of which a voltage rises by the pull-up transistor, cannot rise to a normal voltage level. As a result, a luminance of pixels arranged on a first line in the second block is reduced due to a decrease in a voltage of a first gate pulse generated when the pixels of the second block starts to be driven, and a reduction in the image quality, such as a line dim, may appear. In the shift register, in which an output signal (for example, the gate pulse or the carry signal) of a previous stage is input to a start signal input terminal of a next stage, a reduction in the output characteristic of a stage generating a first gate pulse after the touch sensing period leads to a decrease in voltages of all of gate pulses generated after the first gate pulse. Further, there is no gate pulse generated after the first gate pulse.